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Permanent link (DOI): https://doi.org/10.7939/R3TG85

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Magnetotransport and magnetoresistive anisotropy in perovskite manganites Open Access

Descriptions

Other title
Subject/Keyword
Manganites, Magnetoresistive anisotropy, grain boundary disorder, phase transitions
Type of item
Thesis
Degree grantor
University of Alberta
Author or creator
Egilmez, Mehmet
Supervisor and department
Jung Jan (Physics)
Examining committee member and department
Fenrich Frances (Physics)
Etsell Thomas ( Chemical-materials science engineering)
Jung Jan (Physics)
Alexandrov A.S. (Physics, Loughborough University, UK)
Kravchinsky Vadim (Physics)
Chow Kim (Physics)
Department
Department of Physics
Specialization

Date accepted
2009-06-03T15:32:58Z
Graduation date
2009-11
Degree
Doctor of Philosophy
Degree level
Doctoral
Abstract
We have investigated several topics in the area of manganites including oxygen disorder, grain boundaries, low field magnetoresistance, magnetoresistive anisotropy and magnetic properties. Studied materials were in the form of polycrystalline samples and epitaxial thin films. The studied compounds were Sm(1-x)Sr(x)MnO3 (SSMO) and La(1-x)Ca(x)MnO3 (LCMO). 1-We have studied the effects of oxygen disorder and grain boundary disorder in the SSMO system close to half hole doping level. The temperature dependencies of resistivity and magnetoresistance were measured as a function of the vacuum annealing time. We observed a logarithmic increase of the resistivity as a function of vacuum annealing time. We have shown that an increasing grain boundary disorder softens the magnetic phase transition from a first order phase transition into a second order transition. Furthermore, the peaks in the resistivity and specific heat are broadened and there is an increase in the charge-carrier scattering rates in the metallic state. On the other hand, the polaronic hopping activation energies in the insulating state changed slightly as a function of grain boundary disorder. The origin of these phenomena is discussed. Magnetoresistive anisotropy has been studied as a function of the grain size. Results showed a strong grain size dependence of anisotropic electrical transport in granular samples of manganites. 2-We investigated the anisotropic magnetoresistance (AMR) in ultrathin LCMO films grown on various substrates. It was found that depending on the strain state, the AMR in some of these systems exceeds 100% and can even change sign. These changes are dramatic when compared to the few percent change in AMR in conventional ferromagnets. The mechanism behind these changes in the AMR is discussed. We have also studied the effects of strain on resistive peak broadening with a simple percolation model. We have shown that strain associated with a lattice mismatched substrate in thin films can cause new electronic behavior, not found in bulk materials or thicker films of the same chemical composition. Resistivity of the ultra thin films exhibit strong relaxation effects when measured as a function of time in a constant magnetic field.
Language
English
DOI
doi:10.7939/R3TG85
Rights
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
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